Ask the Expert

Although some animals such as newts and starfish can re-grow lost body parts, spontaneous regeneration of entire human limbs is primarily the subject of science fiction, such as in the TV show “Heroes.”

That being said, there is a lot of promising research going on in the areas of “tissue engineering,” and, more recently, “regenerative medicine.” This is a very exciting time for scientists and engineers who want to help people recover from injuries or illnesses where they have experienced tissue loss or degradation.

Early on, researchers hoped that if we could give cells a physical framework, or scaffold, they would “know” how to fill it in, like ivy crawling up a trellis. That concept has turned out to be a bit naïve, since the scaffolds we can make are not nearly as exquisite as the scaffolds that biology has evolved.

Many of the materials that surgeons currently have available to help their patients look more like something we might find in a sporting goods store rather than in the body. For example, hip joint replacements are made of titanium (like some golf clubs), and coronary bypasses are commonly made with Dacron or GoreTex (fabrics often used for rain jackets). These materials are very far removed from what natural tissues look like, and cells cannot interact with them in a natural way.

Because of this, a current goal in tissue engineering research is to develop scaffold materials that are more like natural tissue, and we have some encouraging new tools. With nanoscience and nanotechnology, we are learning more about how to create materials with fine patterns and features, which is what biology is able to do. Furthermore, we have stem cells. Stem cells are cells that, when properly stimulated, can turn into any other kind of cell. With the increasing availability of stem cells, we may have a readily available source of cells to put on our scaffolds. So we really are at a point where we’ve made substantial advancements in making materials and in developing a self-renewing cell source.

I am involved in several projects where my students, colleagues, and I are trying to make new tissues. In one case we are working on creating scaffolds to regenerate nerve tissue for patients with injured spinal cords. In another, I am working with several other engineering and medical professors to study how to turn stem cells into new heart muscle tissue to fix the damage caused by heart attacks.

In both of these cases, we are focusing on engineering just one kind of tissue. Many people are working on trying to culture, or grow, more than one kind of cell at the same time, but so far scientists have not figured out very good ways to do this yet. Still, that’s what we’d need to do to re-grow a whole limb. Look at an arm, for example. Many different types of tissue can be found in your arm: bone, muscle, nerves, skin, and blood vessels. All of these different tissues have to work together seamlessly.

Currently, we can only make materials that replace a few simple functions of very complex organs. For example, engineered skin is available on the market that can adequately perform real skin’s job as a barrier against the environment. We can also make engineered bone that performs a simple structural role.

What I foresee happening next is making tissue engineered constructs and traditional prosthetics work together better. Maybe if we can grow nerves from the stump of an arm to an interface on a prosthetic arm, we’d be able to improve the transmission of signals between the body and the artificial limb.

Growing new eyes or hands just isn’t possible yet, but we are making great progress toward helping many people in need of a single new tissue.